Windows 7 supports the Trim command.
With your new SSD, use the below to verify that trim is working.
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How do I know if TRIM is working in Windows 7?
In the elevated(right click- run as administrator) command Prompt windows, type the following:
fsutil behavior query disabledeletenotify
Results explained below:
DisableDeleteNotify = 1 (Windows TRIM commands are disabled)
DisableDeleteNotify = 0 (Windows TRIM commands are enabled)
Software like SSDlife Free can also tell if trim is supported and if it is system enabled.
Other than that, I would also check if your drive is aligned. You can run msinfo32 and look if the partition starting offset divisible by 4096 or download AS SSD Benchmark. It should say 'Okay' or 'Bad' under the drive name.